With the continuous promotion of ideas of green environmental protection and low carbon economy around the world, operators have increasingly higher requirements for reducing power consumption in wireless communications systems. In a wireless communications system, a radio frequency power amplifier (power amplifier for short) in a base station device is one of core modules of the entire system. An important indicator of the radio frequency power amplifier is power amplification efficiency. Data analysis indicates that in an entire base station device, energy consumption of a radio frequency power amplifier accounts for about 60% of total energy consumption; and therefore improving power amplification efficiency of the power amplifier becomes the most effective way for reducing power consumption of the base station device and reducing operating expenses of operators.
A Doherty (Doherty) power amplifier is currently a most widely applied high-power power amplifier technology in a wireless communications system. A conventional Doherty power amplifier includes: a main power amplifier, a peak power amplifier, and the like. A basic idea of the conventional Doherty power amplifier is active load pull, which is specifically: The main power amplifier operates in class B or class AB, and the peak power amplifier operates in class C; and each of the two amplifiers bears different input signal power, so that the two power amplifiers both operate in their own saturation regions as much as possible, thereby ensuring that the entire power amplifier maintains relatively high efficiency within an input signal power range as large as possible, and ensuring certain linearity.
However, the inventor finds in researches that in a case where the main power amplifier is biased in class AB, the peak power amplifier is biased in class C, and an impedance transformation relationship is unchanged, the conventional Doherty power amplifier can adjust a drain voltage or a gate voltage in time according to a system service volume, so as to improve efficiency of the power amplifier when power is low; however, according to an actual measurement, when peak power backs off by 12 dB, that is, when output power of the conventional Doherty power amplifier is within a low out power range, an improvement in power amplification efficiency brought about by the foregoing method is less than 10%. Therefore, how to improve power amplification efficiency of a Doherty power amplifier working in a low out power range still has a significant meaning for saving energy and reducing consumption for an entire base station device.